Hot embossing lithography is a powerful method of replicating three-dimensional micro-and nano-structures (see Figure 1) using a stamp that is pressed into a heat-softened polymer resin. Cooling below the glass-transition temperature (Tg) of the polymer cures the motifs and the stamp and substrate are then separated. Successful replication is therefore contingent on interfacial interactions during the embossing phase and most importantly during the separation or release phase. Various organo- and perfluoro-silane release layers have been proposed and studied.

We have employed variable temperature chemical force microscopy (VT-CFM) using tips silanized with four different SAMs interacting with a thin-film of poly(cyclic olefin), (PCO). The silanized-tip/polymer interaction was studied over a temperature range spanning the Tg of the PCO (∼373 K). Adhesion between a saturated hydrocarbon-decorated tip (OTS) and PCO was comparatively strong (170 nN) 30 K above the Tg of the polymer. Adhesion among the perfluorinated tips was 20 to 50 nN lower at 373 K with a relative increase in perfluoromethyl groups (w/w).

Recently, we reported conditions for controllable, direct laser fabrication of sharp conical tips with heights of about one micrometer and apical radii of curvature of several tens of nanometers. An individual cone is formed when a single-crystal silicon film on an insulator substrate is irradiated in air environment with a single pulse from a KrF excimer laser, homogenized and shaped to a circular spot several microns in diameter. In this work, we present a study of the formation of such tips as a function of the laser fluence, the film thickness, and the diameter of the irradiated spot. Atomic force microscopy and scanning electron microscopy were used to study the topography of the structures. A simple mechanism of formation based on movement of melted material is proposed. We have also studied structures (nano-ridges) that resulted from irradiation with narrow lines (width of several microns) instead of circular spots.

In this paper we demonstrate high sensitive and fast response humidity sensors using layer-by-layer (LbL) nano-assembled films of Polypyrrole (PPY). Spin coated PPY films were used for sensitivity and response time comparisons. The change in electrical sheet resistance of the sensing films was monitored as the device was exposed to humidity. For 5% change in relative humidity sensitivity measured from layer-by-layer based devices was 10% and 8% for the spin coated devices. The response time for LbL based and spin coated device was measured as 25 seconds and 57 seconds respectively. The LbL nano-assembled films of PPY showed the better response in terms of sensitivity, response time, linearity and degradation. An intended application for these LbL nano-assembled devices is in disposable handheld instruments to monitor the presence of humidity in humidity sensitive environments.

The fabrication of two-dimensional uniform arrays of microchannels in borophosphosilicate glass (BPSG) layers deposited by plasma-enhanced chemical vapor deposition (PECVD) is presented. The microchannels, with circular cross-sections of 2-3 μm diameter, are formed by depositing specific thicknesses of BPSG over periodic ridge/space templates etched into underlying silica layers using reactive ion etching (RIE). High temperature annealing results in reflow of the BPSG and the formation of uniform circular or cylindrical voids between the template ridges. Control of microchannel size and geometry through process variables is reported, and exploitation of the microfluidic and optical properties of microchannels and integrated waveguides for applications in optical sensing and photonic devices is demonstrated

The discovery of the steep increase of electrical conductivity in Porous Silicon (PS) samples in contact with Nitrogen Dioxide, NO2, opens the possibility to study the electrical conduction processes in nanostructured systems from a completely new point of view. The system undergoes a change of conductivity of 5 orders of magnitude when exposed to few ppm of NO2, whereas the free charge concentration increases by only one order of magnitude in the same pressure range. Upon NO2 exposure the system transition from an “insulator-like” to a “semiconductor-like” behaviour can be studied by means of several techniques. In this paper, the results from a Space Charge Limited Current (SCLC) study unambiguously demonstrate the change of the charging status of defects upon NO2exposure, and explain some “exotic” effects recently reported.

Within this article, a novel in-situ method is proposed as a modification of thermal desorption utilizing pretreatment which can be applied to systems subject to material deposition, substrate heating, and creation of non-oxidizing environments (vacuum or inert atmosphere). Following the theoretical development of this proposed method, involving the fue ling of the oxide-reduction reaction with segregated sacrificial material, the method is demonstrated experimentally on Si (100) wafers utilizing ex-situ atomic force microscopy for resulting surface topography analysis and in-situreflective high-energy electron diffraction for crystalline information during the modified thermal desorption progression.

We investigate the growth of InAs quantum dots on patterned GaAs substrates. The GaAs substrate has been structured using holographic lithography. Quantum dot formation along the patterns has been observed as well as an increase in homogeneity of the quantum dots. Furthermore, the use of ion beams focused to nanometer diameters for substrate patterning has been studied and showed promising results. For the investigation of vertically aligned InAs quantum dots, cross-sectional atomic force microscopy has been successfully employed.

Replica molding of ultra-high-Q toroidal microresonators can produce polymer microresonators with material-limited quality factors (Q). This was demonstrated previously using polymers which cure thermally. In this work, high Q polymer microresonators were fabricated using the replica molding technique from previously uncharacterized polymers which require either a thermal or UV cure. The quality factor and effective refractive index of whispering gallery modes was measured at wavelengths ranging from the visible (680nm) through the near-IR (1550nm). The optical absorption coefficient (material absorption) of these previously uncharacterized polymers was determined from the quality factor and effective refractive index of the polymer.

A lateral contact MEMS switch was developed to address the needs for long life cycle, low contact resistance and low cost switches. The device is unique in its self-cleaning of particles, self-alignment of contact surfaces and the mechanical anchoring of the contact metal into the switch structures. The major issue for the lateral contact device fabrication is the creation of the vertical Au sidewall. Existing physical and chemical vapor deposition methods are found not satisfactory. The final Au sidewalls for electric contact are formed by electroplating in pre-patterned photoresist mold. SEM pictures show that the designed undulated contact surfaces are created successfully, and the surface of the electroplated Au is much smoother and denser than that by e-beam evaporation. The long lifecycle test shows that the contact resistance has been maintained below 0.1 Ω over 1010 cycles. The test results of the fabricated switch have proved the self-cleaning concept and opened the possibility of direct contact MEMS switch for high power and low cost RF applications.

A new simple method for measuring a long-range electrostatic attractive force between metal and semiconductor substrate and charged polymer surfaces has been developed to make clear the effect of the electronic nature of substrate surfaces. Nickel, titanium, and silicon wafer substrates were subjected to various surface pretreatments. The surfaces of polystyrene and polytetrafluoroethylene sheets were positively and negatively charged by triboelectrification, respectively. A progressive increase in the attractive force was observed with a decrease in the distance between the substrate and polymer surfaces. The magnitude of the attractive force was greatly influenced by the substrate pretreatments and the polymers with the oppositely charged surface. The electronic nature of the substrate surfaces evaluated by temperature programmed photoelectron emission method was well correlated with the attractive force. The electrostatic induction generated at the substrate surface is considered to govern the attractive force.

The assembly of plastic microfluidic devices, MOEMS and microarrays requiring high positioning and welding accuracy in the micrometer range, has been successfully achieved using a new technology based on laser transmission welding combined with a photolithographic mask technique. This paper reviews a laser assembly platform for the joining of microfluidic plastic parts with its main related process characteristics and its potential for low-cost and high volume manufacturing. The system consists of a of diode laser with a mask and an automated alignment function to generate micro welding seams with freely definable geometries. A fully automated mask alignment system with a resolution of < 2 μm and a precise, non-contact energy input allows a fast welding of micro structured plastic parts with high reproducibility and excellent welding quality.

Composite semiconductors belonging to the group A1B5C6(Ag3SbS3, Tl3SbS3, Ag3AsS3 and others) are seemed to be among the most promising materials for manufacturing detectors of ionizing radiations (γ-Ray Detectors Based on Composite A1B5C6 Semiconductors, H. Khlyap et al., MRS Proceed. 792 (2004, R3.4.1). Electric properties of these wide-gap semiconductors are almost not studied. The paper reports first experimental results on electric field-induced effects observed in these nanoscaled semiconductor structures under the room temperature. Bulk materials as well as thin films were studied. The experimental data were analyzed according to the semiclassical theory of tunneling in solids.

We present a new route towards customizing the surface properties of microfluidic channels, by a forest of in situ grown multiwalled carbon nanotubes (CNT). Local distortions of the electrical field direction are used to control the direction of the carbon nanotube growth.

The effort to produce an instrument that can achieve high spatial resolution, nondestructive, surface and sub-surface imaging for a variety of materials comes with many challenges. One approach, magnetic resonance-force microscopy (MRFM), lies at the nexus of two sensitive technologies: magnetic force microscopy (MFM) and magnetic resonance imaging (MRI). MFM uses a magnetic tip in a standard atomic force microscope (AFM) to obtain magnetic information about a surface. A difference in the magnetic moments of surface atoms in different regions on the surface varies the cantilever resonance. MRI, on the other hand, uses the spin states of magnetically biased atoms to differentiate between chemical species.

Nickel monosilicide (NiSi) nanowires (NWs) have been fabricated by the metal induced growth (MIG) method. Ni as a catalyst was deposited on a SiO2 coated Si wafer. In a DC magnetron sputtering system, the Ni reacts at 575°C with sputtered Si to give nanowires. Different metal catalysts (Co and Pd) were used to prove the MIG NW growth mechanism. NiSi NWs were a single crystal structure, 20-80 nm in diameter and 1-10 μm in length. The linear NW growth property provided nanobridge formation in a trenched Si wafer. The trenches in a Si wafer were made by dry etching and a simple, conventional metal lift off method. The self-assembled nanobridge can be applied to form nanocontacts at relatively low temperatures. The MIG NB is a promising 1 dimensional nanoscale building block to satisfy the need of ‘self and direct’ assembled ‘bottom-up’ fabrication concepts.

Human ability to manipulate atoms and molecules on quantum basis has generated a new dimension of physical structures for molecular scale transistors and devices. We will discuss about nanodimensional single electron transistor. This molecular device works as a switching element by controlling the electron tunneling for amplifying the current. The basic structure consists of two tunnel junctions isolated by a common insulator of nanodimensional length.

One broader aspect of nano power electronics is that, it has got significant role in nanodimensional device regime as tunneling diodes. They have got inherently fast tunneling rate, which makes them highly suitable for high-speed operation. A special type of tunneling diode is an interband tunneling diode (ITD), which is actually, a p-n diode. The V-I characteristics of such diodes are dependent upon the tunneling barrier and tunneling process itself. Another special feature of these diodes is their negative-differential-resistance characteristics. This special characteristic of such diodes makes them very useful in switching digital circuits.

The improvement of nanofabrication is one of the driving forces behind advancements in the fields of electronics, photonics and sensors. Precise control over nanoscale architecture is an essential aspect in relating new size-dependent material properties. Direct writing methods such as Electron Beam Lithography (EBL), enable precise “user-defined” writing of nanostructures in a wide range of materials. Using electrodynamics calculations, Schatz and coworkers have discovered one dimensional array structures built from spherical silver nanoparticles that produce remarkably narrow plasmon resonance spectra upon irradiation with light that is polarized perpendicularly to the array axis. In order to investigate these interactions, precise control of nanoparticle orientation, size, shape and spacing is necessary. If the overall structures have excessive defects then the effect may not be seen. To have the best control over array fabrication and to look at these interactions experimentally, EBL was used to construct lines of circular cylinders of varying interparticle spacings. Dark field microscopy was used to look at overall sample homogeneity and collect the single particle plasmon resonance spectrum. Additionally, a UV-visible spectrometer with a variable angle stage was used to look at the bulk line properties. With experimental verification of the theory will lead to not only a more thorough understanding of the underlying principles of nanophotonics, but also application in biosensing, that potentially improve on current technologies.

In this paper we describe an oxide molded tungsten process applied to the fabrication of a novel latching relay. The steps in the process are: deposition of a sacrificial oxide, patterning of the oxide, filling of the resulting mold with a blanket film of tungsten using chemical vapor deposition (CVD), and then the removal and planarization of excess tungsten through chemical mechanical polishing (CMP). The process for the incorporation of dielectric isolation has also been developed. The resulting tungsten structures are under high tensile stress, which appears to be compensated in process by the compressive stress of the oxide mold. All the steps are low temperature and the entire process is backend CMOS compatible. This process has been used to fabricate a latching relay which relies on the internal stress of the tungsten and always generates force in a pulling mode. Parts have been successfully fabricated and tested, the devices generate very high forces for a MEMS device and give reasonable contact resistances even without noble metal contacts.